Modeling a solid-phase electrochemical reaction of lithium intercalation in aluminum during a noninstantaneous nucleation of Β-LiAl

The interfacial surface area and the electrode surface coverage by a product during the nucleation and growth of a new phase are modeled numerically and calculated analytically for electrochemical intercalation of lithium in aluminum in the course of which intermetallic compound Β-LiAl forms. As opposed to the theoretical calculation, the model accounts for mutual influence of the new-phase nuclei on their distribution over the cathode surface under conditions of noninstantaneous nucleation. The ordering of such a distribution varies extremally (passes through a maximum) with increasing size of zones where the nucleation probability is low and which surround the nuclei. This makes the dependence of a maximum specific interfacial area on the zone radius extremal as well. The model may be applied for analyzing potentiostatic current transients during cathodic intercalation of lithium in aluminum from a LiClO₄ solution in propylene carbonate.     

Linear Preservers of Extremes of Rank Inequalities over Semirings: The Factor Rank

We characterize linear preservers for sets of matrix ordered tuples which satisfy extremal properties with respect to factor rank. __________ Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 13, Algebra, 2004.     

PtM/C (M = Ni,Cu, or Ag) electrocatalysts: effects of alloying components on morphology and electrochemically active surface areas

The microstructures of Pt/C and PtM/C (M?=?Ni, Cu, or Ag) electrocatalysts were studied using X-ray diffraction and transmission electron microscopy (TEM). The electrochemically active surface areas of the prepared materials were estimated by cyclic voltammetry in 1 M H₂SO₄. The materials, with metal contents ranging from 30 to 35 wt.%, were synthesized by chemically reducing the metal precursors in water–ethylene glycol solutions. The actual composition of the bimetallic nanoparticles corresponds to a theoretical (1:1) composition for the PtAg/C catalysts, whereas in the PtNi/C and PtCu/C materials, a portion of the alloying component exists in an oxide form. Decreasing the average metallic crystallite sizes from 3.5 to 1.6 nm does not increase the electrochemically active surface area. This apparent contradiction is because a majority of the PtNi and PtCu nanoparticles consist of 2–4 disordered crystallites. In addition, a portion of the PtNi or PtCu nanoparticle surface is covered by nickel or copper oxides, respectively. PtAg nanoparticles, which have a smaller size relative to other bimetallic particles according to the TEM data, are characterized by an intense platinum surface segregation. The agglomeration processes are lowest for the PtAg nanoparticles.     

Electronic and atomic structure of platinum-cobalt nanocatalysts

X-ray diffraction in combination with X-ray emission and EXAFS spectroscopy were used to study the electronic and atomic structure of metal nanoparticles stabilized on a carbon support in novel Pt _x Co/C catalysts of different composition with the molar ratio Pt:Co (x) of 1 to 3. Cobalt atoms in nanoparticles, which average size was 2–4 nm, were shown to form chemical bonds both with platinum atoms and carbon atoms of the support material.     

Microstructure and electrochemically active surface area of PtM/C electrocatalysts

The results of the study of microstructural parameters and the data on the electrochemically active surface area of Pt/C and Pt₅₀M₅₀/C (M = Ni, Cu, Ag) catalysts in 1 M H₂SO₄ solutions are compared. The metal-carbon nanomaterials were prepared by the method of chemical reduction of metals from the organoaqueous solutions of their compounds. The loading of metal component in them was 30–33 wt %. It is found that actual composition of metal component in the synthesized binary systems fits best the theoretically expected one (1: 1) for the PtAg/C catalyst whereas in the PtNi/C and PtCu/C systems, a considerable fraction of alloying component is present in the form of the corresponding oxides. A decrease in the average size of crystallites of metal component from 3.8 to 1.6 nm in the series of studied materials PtAg/C > Pt/C ≥ PtCu/C s> PtNi/C does not correspond to the character of the variation of electrochemically active surface area of the catalysts: PtNi/C ≈ PtCu/C < Pt/C ≪ PtAg/C increasing from 16–20 to 62–69 m²/g(Pt). The contradiction can be caused by the preferential segregation of platinum on the surface of nanoparticles of PtAg alloy, a higher degree of agglomeration of smaller nanoparticles, and, in the case of PtNi/C and PtCu/C materials, also by the insulation of a fraction of nanoparticle surface area by the corresponding oxides.     

De-Alloyed PtCu/C Catalysts of Methanol Electrooxidation

Russian Journal of Electrochemistry - The activity of PtCu/C catalysts in methanol electrooxidation is studied in HClO4 solution. The electrochemical behavior of catalysts is compared for samples...     

Maps preserving scrambling index

In this paper we characterize bijective linear maps on matrices over semirings that preserve scrambling index.     

Platinum Electrocatalysts Deposited onto Composite Carbon Black–Metal Oxide Support

Russian Journal of Electrochemistry - New nanostructured Pt/(SnO2/C)-electrocatalyst (20 wt % Pt) is synthesized via platinum chemical deposited onto composite SnO2/C-support microparticles (4 wt %...     

Studying the Initial Stage of Nucleation and Growth of a New Phase during Cathodic Intercalation of Lithium into Aluminum

Kinetics of cathodic intercalation of lithium into aluminum from a 0.5 M LiCl solution in dimethylformamide at the stage of nucleation and growth of intermetallic compound -LiAl is studied by one- and two-pulse potentiostatic methods. If the length of the first potential pulse is short, the current at the beginning of the second pulse is proportional to the overvoltage squared. The experimental data point to a lamellar-spiral growth of -LiAl crystals at the initial stage of their development and to a change in the balance between different growth mechanisms as a function of the overvoltage and surface coverage by -LiAl.